1. Field of the Invention
The presently disclosed subject matter relates to a method for manufacturing a coating film. More particularly, the presently disclosed subject matter relates to a method for manufacturing a coating film in which a coating layer is provided by applying a coating liquid to a travelling plastic film.
2. Description of the Related Art
In a flat panel display (FPD), including a cathode-ray tube display (CRT), a plasma display panel (PDP), an electroluminescent display (ELD) and a liquid crystal display (LCD), an optical functional film (coating film), such as an antireflection film, an antiglare film or a surface protection film, is used for the outermost layer of the flat panel display, in order to enhance visibility and improve abrasion resistance.
The abovementioned optical functional films are frequently and directly exposed to human visual observation. In addition, there has recently been a significant increase in the screen size, brightness and definition of displays. Consequently, an optical functional film to be used is stringently required to have appearance quality (absence of point defects, uneven coating, contamination, and the like) and quality in terms of physical durability (superiority in abrasion resistance, stainproofness, and the like).
In particular, abrasion resistance is crucial for an antireflection film since if a display surface becomes scratched, the scratch leads to a permanent display defect, thus causing the appearance quality of a display unit to degrade significantly.
The optical functional layer of the antireflection film is generally formed by repeating a process of coating a solution of a material for forming functional materials containing an organic solvent onto a base film and drying the solution a plurality of times. In the course of manufacturing an optical film in which the optical functional layer is provided by such a coating process as described above, an appearance failure (unevenness failure, in particular) is liable to occur due to irregularity in the coating liquid immediately after coating or irregularity in the coating thickness of the optical functional layer caused by nonuniform drying.
Accordingly, in order to improve coating properties, uniformize drying and impart high-speed coatability, there has been proposed a method for adding an additive, such as a fluorine-based compound or a silicone-based compound having an interfacial activation effect, into the coating liquid (see Japanese Patent Application Laid-Open No. 2005-257786). In addition, a method has been carried out in which drying speed at the time of initial drying is controlled and contactless feed is performed. (See Japanese Patent Application Laid-Open No. 2006-334561).
On the other hand, as a method for imparting abrasion resistance, there is known a method in which a coating liquid composed primarily of an ionizing radiation-cured resin composite including fine particles is coated and hardened using ultraviolet rays, electron beams or heat, when forming a low-refractive index layer to be located on the outermost surface (Japanese Patent Application Laid-Open No. 9-145903). In addition, the antireflection film is formed by laminating a plurality of optical functional layers and physical functional layers. Hence, reactive functional groups in the hardening resin of a layer to be coated are brought into a half-cured state, in order to improve interlayer adhesion (Japanese Patent Application Laid-Open No. 2003-311911).